1. Field of the Invention
The present invention relates to a standard specimen for a charged particle beam apparatus and relates in particular, in the occasion of carrying out length measurement of a specimen to be observed with an electron microscope, to a standard specimen for electron microscope measurement calibration enabling measurement of several ten μm or smaller micro size with high precision and a method for preparation thereof.
2. Description of Related Art
A scanning electron microscope is an apparatus of magnifying the specimen shape in an order of several hundred to several tens of million to form an image. In order to carry out precise calibration of magnification and length measured value of an image, for example, in the case of a Scanning Electron Microscope (SEM), a micro scale being a standard specimen having a pitch pattern, a size of which is known, is used to calibrate measurement in magnification in an order of fifty thousand-fold to several hundreds of thousand-fold. With respect to a specimen for measurement calibration of a scanning electron microscope, an example of length measurement calibrating member is described in JP-A-7-071947. In addition, an example of measurement calibrating specimen is described in JP-A-8-031363, Yoshinori Nakayama “Semiconductor Pattern Metrology with Electron Beam”, The Journal of the Japan Society for Precision Engineering, Vol. 68, No. 3, 2002 and I Misumi, et al. “Uncertainty in pitch measurements of one-dimensional grating standards using a nanometrogical atomic force microscope”, Meas. Sci. Technol. 14 (2003) 463-471. Moreover, an example of nanometrological calibration secondary standard specimen is described in JP-A-2003-279321.
On the other hand, in the case of a transmission electron microscope (TEM) and a scanning transmission electron microscope (STEM) carrying out observation with electrons transmitting a specimen, sizes on necessary sites are measured with the crystal lattice image, a size of which is already known, as a standard in magnification of several million-folds or more. A standard specimen for such an object, which is provided with a multi-layer film of Ge on a Si substrate and is prepared with an ion thinning method, is put on the market by Norrox Scientific Ltd (CANADA).
The measurement calibrating calibration member for a scanning electron microscope disclosed in the above described patent documents is not a film specimen for an electron beam to transmit and is not applicable for measurement calibration of (Transmission Electron Microscope: TEM) and Scanning Transmission Electron Microscope: STEM carrying out observation with electrons having transmitted the specimen.
In the case of the prior arts to carry out image observation utilizing the above described other transmission electrons, in order to observe crystal lattice images between 0.2 nm and 0.3 nm such as metal, it is necessary to set a TEM to provide 0.3 million-fold magnification, to set a TV camera to provide approximately ten-fold magnification and lastly to provide not less than three million-fold magnification. In addition, in the case of a STEM, it is necessary to set magnification of three million-fold or more. Therefore, in the case of magnification of not more than several million-folds allowing observation of no lattice image, a structure to be observed undergoes length measurement with a lattice image as a standard to provide magnification three million-fold or more. Then secondary length measurement is carried with the structure as a standard. However, the above described structure to be observed does not always fall in the desired region for observation. In such a case, there is no means for precise magnification and length measurement value calibration on images.
In addition, a standard specimen of the above described prior arts is prepared by the ion thinning method to prepare thin film by applying Ar+ ion beam with several nm diameter.
In that case, a wide region undergoes thin-filming to give rise to deflection frequently. Therefore it is difficult to measure line width of multilayer film to become a precise standard.